EXTENDED SPEED RANGE (ESR) EFFECT

We are using the term ESR effect (Extended Speed Range effect) to define a fixed pitch propeller (or ground adjustable pitch one) which behaviour is near from the behaviour of a variable pitch propeller.

This ESR effect has the following characteristics : it causes very small gap between the static RPM and the flight RPM, and this allows to keep a strong power at take-off.
It seems that the max throttle RPM stays nearly constant.

Example for a ROTAX 912 engine, for 5.800 RPM at 120 km/h :
- a propeller not ESR will have between 600 and 1000 RPM less at take-off, and its thrust will be lower than 185 kg
- a propeller with ESR effect will allow to have only 200 RPM less at take-off (5600 RPM), it means a static thrust of 210 kg (10 % more!)

The ESR effect can improve the performances at take-off, because then the engine is running very near of its max RPM, and provide all its power during take-off.
Some E-Props models allow to have more RPM at take-off than in flight...

From technical point of view, there are different solutions to obtain this ESR effect :
- narrow chord with classic profiles
- pitch reduction at low speed by blades deformation (difficult to obtain)
- narrow chord with special profiles, in order to avoid the stall of the blades => it is the case of E-Props propellers